Clean SQL Server Cache

2012/04/06

I lives alone, usually, I clean my small apartment at every weekend, wipe the table/firniture with cloth, clean the capet with vacuum cleaner, wash clothes with machine. the clea enviroment makes me feel confortable, and have a good start for the new week.

SQL Server memory cache just like an apartment(or house?), before we start testing , we'd better clean the memory cache first. just like we clean the house, we use tools to clean cache as well.

1. DBCC FREESYSTEMCACHEBOOK ONLINE: manually remove unused entries from all caches or from a specified Resource Governor pool cache. it has 2 parameters, the format is like:DBCC FREESYSTEMCACHE ('ALL','default');

this is only the sample in BOOK online, there is no more description of the parameter. then I searched the parameter, here are some findings:

Clean all caches

DBCC FREESYSTEMCACHE ('ALL')

sometimes if you can not shrink the tempdb log file, and get the error below:“DBCC SHRINKFILE: Page X:xxxxxxx could not be moved because it is a work table"

so it is better to run checkpoint before run DBCC DROPCLEANBUFFERS, checkpoint will write all dirty pages back to disk, so you can release more buffer pool space

3. DBCC FREEPROCCACHERemoves all elements from the plan cache, removes a specific plan from the plan cache by specifying a plan handle or SQL handle, or removes all cache entries associated with a specified resource pool

I think it is similar with "DBCC FREESYSTEMCACHE ", but it can only clean plan cache, and it provide parameter to let you control the clean more detail. you can specify the planid and pool name.also this command has less impact than "DBCC FREESYSTEMCACHE ", MVP Glenn Berry mentioned the impact of FREEPROCCACHE is "pretty minor", and it is useful for some senarioshttp://www.sqlservercentral.com/blogs/glennberry/2009/12/28/fun-with-dbcc-freeproccache/

4. DBCC FLUSHPROCINDB (@intDBID);Flush the procedure cache for one database only

5. DBCC FREESESSIONCACHEFlushes the distributed query connection cache used by distributed queries against an instance of Microsoft SQL Server.

so if you want to make a completely clean on the cache, you can try Rajesh Chandras 's scriptDBCC FREESYSTEMCACHE(All)DBCC FREESESSIONCACHEDBCC FREEPROCCACHEDBCC FLUSHPROCINDB( db_id )CHECKPOINTDBCC DROPCLEANBUFFERS